Short pulse generator



g- 5, 1958 H. G. PURINTON ,Mfifi? v SHORT PULSE GENERATOR Filed Sept.20, 1954 HAROLD s. PURINTON 2 .INVENTOR.

M ATTORNEYS snonr PULSE GENERATOR Harold G. Purinton, Baltimore, lVId.,assignor to Bendix Aviation Corporation, Towson, Mi, a corporation ofDelaware Application September 20, 1954, Serial No. 456,989

Claims. (Cl. 250-27) This invention relates to pulse generators and moreparticularly to a pulse generator capable of producing pulses of veryshort duration.

In some situations it is desirable to produce pulses of durations of ahalf microsecond or less and having fast rise and decay times. Amongother expedients which have been tried for this purpose, use has beenmade of a thyratron oscillator having a series resonant circuitconnected between the plate and cathode thereof. While such circuitshave been able to produce pulses satisfactory for some purposes theyare, however, subject to the defect that when coupled to a load circuitwhich has substantial capacity to ground the very high frequencycomponents of the pulse are lost and the form of the pulse is thusaltered so that it has rise and decay slopes less steep than might bedesired.

It is an object of this invention to provide a pulse generator capableof producing extremely short pulses having very fast rise and decaytimes.

It is a further object of the invention to improve the thyratronoscillator type of pulse generator circuit in a manner which enables itto provide pulses of shorter duration and having faster rise and decaytimes than has heretofore been possible.

These and other objects of the invention are realized by a circuit inwhich the series resonant circuit is connected for R. F. across the loadimpedance of the thyra tron, rather than across the plate cathode spaceof the tube. Two forms of the circuit may be utilized, in one of whichthe load resistor is in the plate circuit, and the other of which it isin the cathode circuit of the thyratron. In the former version anegatively polarized output pulse will be obtained, whereas in thelatter version the output pulse will be positive going. The capacity ofthe series resonant circuit is so selected that it, in conjunction withthe capacitance to ground of the load circuit into which the output ofthe generator is coupled, will cause the formation of a pulse of thedesired duration. in practice the lumped inductance is made small sothat the ratio of lumped capacitance to load capacitance will be large,thus producing stability in pulse duration with varying load capacities.

in the drawing, Fig. 1 is a schematic diagram of a circuit embodying theinvention and arranged to produce negatively polarized output pulses;

Fig. 2 is a schematic diagram of a circuit similar to that of Fig. l,but arranged to produce positively polarized output pulses.

Referring now more particularly to the drawing, there is shown in Fig. 1a thyratron 1. Triggering voltage is applied to the thyratron from aterminal 2 by way of a resistor 3. The terminal 2 is also connected toground by a resistor 4. The cathode is connected to the positiveterminal of a source of supply voltage by Way of a resistor 5'. Thecathode is also connected to ground through a resistor 6, the lowerterminal of which is connected to a slider '7 for varying the value ofthe resistor 6. The anode is connected to a load resistor 8, theremaining 'thyratron.

terminal of which is connected to the positive terminal of the supplyvoltage source. A connection is returned from the latter terminal to aslider 9 for varying the value of the resistor 3. The anode is alsoconnected by way of a capacitor 10 and a coil 11 to the cathode. Thejunction of the coil 11 and the cathode is connected to ground by way ofa capacitor 12. The coil is by-passed by a diode 13. The junction of thecoil 11 and the capacitor 10 is indicated as the point 14, at which theoutput of the generator appears and from which it is applied to a loadcircuit indicated by the box 17. The capacity to ground of this circuitis indicated by the dashed line capacitor 18.

In the operation of the above described circuit a triggering pulsehaving a waveform as indicated in the graph 15 is applied to terminal 2.This pulse should have a duration at least as great as the ionizationtime of the thyratron being used and its application causes ionizationto occur within the tube. The ionization causes the anode to rapidlylose its positive potential because of the IR drop across the resistor8. This sharp voltage drop is applied to the series resonant circuitconsisting of the capacitor 10 and the coil 11 and the action of thatcircuit in conjunction with the capacitance 13 forms the negative goingoutput pulse having a waveform as indicated by the graph 16, which pulseappears at 14 and is applied to the load circuit 17. The value of thecapacitor 12 connecting the junction of coil 11 and the cathode of thethyratron to ground is so selected as to provide an R. F. ground forthat end of the coil. The voltage supply source must be shunted bysufiicient capacity to provide a low impedance to ground for R. F. Thediode l3 shunting the coil 11 has the effect of damping out the positivegoing swing of the waveform so that only the initial half cycle of theoscillation is recovered as indicated by the graph 16. In operating witha load circuit having a small value of capacity to ground the value ofthe inductance of the coil 11 can be made quite small and the ratio ofthe capacitance 10 to the load capacitance 13 can be made large. Achoice of values of 10 and 11 in conjunction with capacitance 38 can bemade, such that the pulse duration is very small and stable in length.The capacitor 12 furnishes a high frequency ground reference to seriescircuit 10, 11 and a low impedance source of electrons to the thyratro-ncathode. The dashed line capacitor 25 represents the low impedance ofthe power supply to R. F. currents.

in the form of the invention illustrated in Fig. 2 the load impedance ofthe tube has been changed from the anode circuit to the cathode circuitand appears as a resistor 19, made variable by means of a slider 26connected to its grounded terminal. The resistor 5 is in this form ofthe invention connected to a slider 21 on a resistor 22, which isconnected between the positive terminal of the supply voltage andground. The anode of the thyratron is connected to ground by way of acapacitor 23. The series resonant combination of capacitor 10 and coil11 are connected across the cathode load resistor 19. The coil isshunted as before by a diode 13 which has its cathode connected to thejunction of capacitor 10 and coil 11.

In the operation of this circuit the positive triggering voltage 15 isapplied as before to the input circuit of the The resulting ionizationof the thyratron causes an IR rise in the cathode circuit resulting inthe formation of an output pulse 2 having the same shape as the pulse 16but being of a positive polarity. Otherwise, the operation of thecircuit is the same as the operation described above for the circuitillustrated in Fig. 1. The duration of the pulse is controlled as beforeby the selection of the values of capacitor 10 and coil 11 inconjunction with load capacitance l8.

In each of the circuits of Figs. 1 and 2 the equivalent circuit of thepulse forming network is constituted by the series resonant circuitconnected in series with the load resister of the thyratron.Thecapacitors 12 and 25 of Fig. 1 and 23 of Fig. 2 act to form a lowimpedance path for R. F. currents across the bias resistor 6 and thepower supply respectively, acting to provide a low impedance.

path for radio frequencies around all elements of impedance in serieswith the gas discharge path of the tube, except those in the pulseforming network thus afiording the utilization of the higher frequencycomponents of the generated pulse which would otherwise be unavailable.

By the use of the circuits described above pulses having extremely shortdurations may be obtained. These pulses may be clipped to any desiredheight by the use of cathode coupled clippers or biased diodes in amanner known to the art, thus producing square waves of extremely shortduration and of very low rise and decay times.

What is claimed is:

1. A pulse generator comprising a gas discharge tube having a plate, acathode and a control grid, a load resistor and a power supply connectedin series with the gas discharge path of said tube between said plateand said cathode and constituting elements of impedance in said path, aseries resonant circuit connected between said plate and said cathode toconstitute a pulse forming network, a load circuit connected to saidseries resonant circuit, said load circuit having a capacity to ground,said capacity to ground acting as an integral part of the pulse formingelements of said resonant circuit, means damping the output of saidseries resonant circuit only after the first half cycle of theoscillation thereof, means forming a low impedance path for radiofrequencies across all elements of impedance in series with the gasdischarge path of said tube except those of the said pulse formingnetwork, thus aifording greater utilization of the high frequencycomponents of the generated pulse, and means applying a pulse of energyto said control grid of said gas discharge tube.

2. A pulse generator as claimed in claim 1, said load resistor being inthe plate circuit of said gas discharge tube.

3. A pulse generator as claimed in claim 1, said load resistor being inthe cathode circuit of said gas discharge tube.

4. A pulse generator as claimed in claim 1, said means forming said lowimpedance path for radio frequencies across said elements comprising acapacitor connected across each of said elements.

5. A pulse generator comprising a serially connected capacitor, inductorand switching device for initiating a predetermined change of state ofcharge on said capacitor, a unilaterally conductive damping deviceconnected across said inductor, the connection between said inductor andsaid clamping device being so poled that said damping device willconduct only upon reversal of the potential across said inductorinitially established by the operation of said switching device, anelectrical biasing network serially connected with said switchingdevice, said network having at least two impedance segments, a loadcircuit connected to the junction of said capacitor and said inductorand a junction of said two segments of said biasing network and aby-pass capacitor having avalue of capacity larger than said first namedcapacitor, one terminal of which is connected to the last named junctionand the other terminal of which is connected to the junction betweensaid biasing network and said switching device most remote from theconnection between the first named capacitor and said switching device.

References Citedin the file of this patent UNITED STATES PATENTS2,391,894 Gorham et a1 Jan. 1, 1946 2,398,701 Firestone Apr. 16, 19462,464,279 Zarem et al Mar. 15, 1949 2,555,305 Alty June 5, 1951

